The disclosure relates to automatic transmissions that shifts power applied to an input member and output the shifted power to an output member.
In recent years, in order to improve fuel economy and acceleration performance of vehicles, multi-speed automatic transmissions have been developed as stepped automatic transmissions that are mounted on the vehicles. An automatic transmission that attains twelve forward speeds and a reverse speed by using four planetary gear mechanisms and six engagement elements comprised of three clutches and three brakes is conventionally proposed as such a stepped automatic transmission (see US 2010/0144486).